
Antimicrobial peptides (AMPs) are short sequences of amino acids, typically fewer than 50 amino acids, that exhibit strong antimicrobial activity against a wide range of microorganisms1). In the oral microbiome, AMPs are critical components of the innate immune system and serve as the first line of defense against harmful microorganisms2). Several AMPs, including histatins, defensins, and LL-37, have been found in the oral epithelium and saliva, and are considered key components of the oral defense system3-10). Additionally, these naturally occurring AMPs are host defense peptides that regulate the innate immune response of host cells and exhibit resistance to oral pathogenic microorganisms11). AMPs can be classified into various types based on their structure, such as alpha-helical, beta-sheet, looped, or extended peptides, with these structural characteristics closely related to their antimicrobial activity and mechanism of action12). Most AMPs are positively charged and possess amphipathic properties, indicating that they contain both hydrophilic and hydrophobic regions. This property is crucial for their interaction with microbial cell membranes12,13). These peptides exhibit broad-spectrum antimicrobial activity, allowing them to target a wide range of pathogenic microorganisms, including bacteria and fungi14). AMPs insert themselves into microbial membranes and form pores that disrupt membrane integrity, leading to cell lysis and death13,15). Some AMPs can penetrate microbial cells and interfere with critical processes such as DNA, RNA, or protein synthesis14,16-18).
The antimicrobial mechanism of AMPs begins with non-specific interactions with components of the bacterial membrane, such as negatively charged phospholipids, lipopolysaccharides, and teichoic acids19-21). When peptides are inserted into the lipid bilayer, the barrier function of the bacterial membrane is compromised, resulting in the loss of membrane potential, leakage of cytoplasmic components, and eventually cell death13,14,22,23). In addition to directly killing pathogens, AMPs can modulate immune responses by recruiting immune cells to infection sites and promoting the production of other immune molecules24).
The human body naturally produces AMPs in various parts of the oral cavity, including saliva, oral mucosa, and oral tissues25,26). These peptides are produced by various cells in the oral cavity, particularly epithelial cells, neutrophils, and salivary glands26,27). Key examples include defensins, cathelicidins (e.g., LL-37), histatins, calprotectin, and lactoferrin3-10,28-30). Defensins are essential AMPs in the oral cavity and are classified into α-defensins and β-defensins31). The α-defensins are primarily secreted by neutrophils and function to kill or inhibit bacteria, viruses, and fungi in the oral cavity3,31). β-Defensins are secreted by the oral mucosa and serve as a primary defense mechanism of the oral epithelial cells4-6,31). β-Defensin-2 and -3 are commonly found in the oral cavity and exhibit strong defense capabilities against not only bacteria but also some viruses4,5). Cathelicidin, also known as LL-37, is secreted by oral epithelial and white blood cells7). LL-37 exhibits antimicrobial activity against bacteria, viruses, and fungi found in the oral cavity. It also helps to regulate inflammation and promotes cell regeneration and tissue repair6-8).
Histidine-rich peptides (histatins) are mainly secreted by salivary glands9,10). Histatin-5 is a representative AMP with strong activity against fungi and plays a significant role in inhibiting oral fungal infections, such as Candida albicans10). In addition, histatins promote wound healing9). Calprotectin is an antimicrobial protein primarily secreted by white blood cells32). It inhibits bacterial and fungal growth by blocking metal ions28,32). This peptide exhibits antimicrobial activity, particularly against bacteria in the oral cavity28). Lactoferrin is a protein present in saliva that binds iron, preventing bacteria from utilizing it and thus inhibiting bacterial growth29,30). It is particularly effective against cavity-causing bacteria such as Streptococcus mutans29,30).
Some bacteria in the oral microbiome produce their own AMPs, known as bacteriocins, which help them compete with other microbial species33,34). AMPs selectively target pathogenic microorganisms, maintaining the balance of the oral microbiome while allowing beneficial (commensal) bacteria to thrive14,35). This selective action is crucial for preventing infections and preserving the beneficial microbial community that supports oral health35). When the balance of the oral microbiome is disrupted by poor oral hygiene, diet, or systemic health issues, the production and activity of AMPs can be altered28). This alteration can lead to the overgrowth of pathogenic bacteria, contributing to conditions such as gingivitis and periodontitis28,36). Owing to their potent antimicrobial properties and ability to modulate the immune response, synthetic AMPs are being studied for therapeutic use in the treatment of oral infections and diseases37). Synthetic or modified AMPs can be developed to enhance oral health by targeting specific pathogens without disturbing the overall microbiome37,38).
Synthetic or natural AMPs can be used in mouthwashes or dental treatments to prevent or treat infections38-40). The development of oral implant coatings and dental restoratives using AMPs represents an advanced biotechnological approach aimed at preventing infections and promoting oral health41). By applying these peptides to oral implants and dental restoratives, issues related to oral cavity infections can be effectively addressed41). Oral implants carry a risk of infection after surgery, and if an infection occurs, the risk of implant failure increases42). Coating implant surfaces with AMPs can help prevent post-implantation infections. AMPs have minimal side effects, increasing the biocompatibility of implants and helping to prevent periodontal diseases and other oral inflammations, thus improving implant success rates41).
Dental restoratives are used to repair decayed and damaged teeth. Using restoratives embedded with AMPs can inhibit bacterial growth around the restoration and prevent the recurrence of cavities43). The peptides combined with the restorative material can suppress bacteria such as S. mutans, the main cause of cavities, thus preventing cavity recurrence after treatment43). Some AMPs stimulate tissue regeneration, aiding the recovery of tissues surrounding the restored tooth and ensuring long-term oral health41,44,45). Restoratives containing AMPs resist microbial degradation, thereby prolonging the lifespan of the restorative material43).
AMPs are essential for oral health and act as natural antibiotics that help regulate microbial populations, prevent infections, and maintain a healthy balance within the oral microbiome2,13-18,46). The advantages of using AMPs as dental materials include their ability to act against various oral pathogens without causing resistance, even after long-term use38-41,43). However, disadvantages include the high cost of producing AMPs, concerns about how long these peptides can maintain their antimicrobial properties in dental environments, and how safely they degrade in the body41). Current research on implant coatings and dental restoratives using AMPs is actively progressing, with a focus on improving their stability and effectiveness41). AMPs are thought to offer a promising solution for peri-mucositis and peri-implantitis that may arise after dental implants and restorative treatments.
This review summarizes research related to AMPs found in the oral cavity to understand their amino acid sequences and antimicrobial mechanisms. Additionally, it organizes previous studies on the use of synthetic AMPs to eliminate oral pathogens in tabular form. By analyzing these summarized results, this review explores the potential for utilizing synthetic AMPs, originally discovered outside the oral cavity, in oral care products, implant coatings, and dental restorative materials. The focus is on natural AMPs as alternative therapeutics for oral infections, such as dental cavities, thrush, and periodontitis. This review also examines both the current use of natural AMPs and the development of their synthetic counterparts for targeting oral pathogens.
A literature search was performed using PubMed (https://pubmed.ncbi.nlm.nih.gov/) and Google Scholar (https://scholar.google.com/). The keywords used for the search were “Antimicrobial peptide (against oral pathogens),” “Dental implant with peptide coating,” “Application of peptide in oral hygiene,” and related terms. Studies that were not focused on oral pathogens or oral hygiene, as well as those centered on antibiotics other than AMPs, were excluded. Following this selection process, a total of 66 articles were collected, and their content was analyzed and summarized.
The amino acid sequences of AMPs were retrieved from the NCBI (National Center for Biotechnology Information) database (https://www.ncbi.nlm.nih.gov/guide/proteins/) and UniProtKB (https://www.uniprot.org/).
Various AMPs are secreted within the human oral environment (Table 1)3-10,28-30,47-54). Cystatins are natural inhibitors of cysteine proteinases and are found in various human tissues and body fluids55). Several studies have shown that cystatins possess antiviral and antibacterial properties. For instance, a tripeptide derivative of cystatin C has demonstrated antibacterial effects against group A streptococci, while phosphorylated rat cystatin α has been found to hinder the growth of Staphylococcus aureus56). Salivary cystatins suppress the growth of Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans47,48). Blancas-Luciano et al.49) demonstrated that cystatin C inhibited the growth of P. gingivalis without exhibiting cytotoxicity against human gingival fibroblasts.
Natural Antimicrobial Peptides in the Oral Cavity
Peptide name | Origin | Peptide sequence | Target | Reference | |
---|---|---|---|---|---|
Alpha-defensins HNP 1-4 (α-defensins) | Neutrophils, gingival sulcus, sites of inflammation, salivary duct cells | HNP1 | ACYCRIPACIAGERRYGTCIYQGRLWAFCC | Candida albicans | 3) |
HNP2 | CYCRIPACIAGERRYGTCIYQGRLWAFCC | ||||
HNP3 | DCYCRIPACIAGERRYGTCIYQGRLWAFCC | ||||
HNP4 | VCSCRLVFCRRTELRVGNCLIGGVSFAYCCTRV | ||||
Cystatins | Human tissues, body fluids | Cystatin C | GGPMDASVEEEGVRRALDFAVGEYNKASNDMYHSRALQVVRARKQIVAGVNYFLDVELGRTTCTKTQPNLDNCPFHDQPHLKRKAFCSFQIYAVPWQGTMTLSKSTCQDA | Porphyromonas gingivalis Aggregatibacter actinomycetemcomitans | 47-49) |
Cystatin SA | MAWPLCTLLLLLATQAVALAWSPQEEDRIIEGGIYDADLNDERVQRALHFVISEYNKATEDEYYRRLLRVLRAREQIVGGVNYFFDIEVGRTICTKSQPNLDTCAFHEQPELQKKQLCSFQIYEVPWEDRMSLVNSRCQEA | ||||
Dhvar4a | Salivary glands | KRLFKKLLFSLRKY-NH2 | Streptococcus mutans Streptococcus sobrinus | 51) | |
LL-37 | Neutrophils, gingival sulcus, salivary glands and ducts | LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES | S. mutans Fusobacterium nucleatum A. actinomycetemcomitans P. gingivalis Capnocytophaga sputigena Staphylococcus aureus | 6-8) | |
β-defensins: hBD1, hBD2, hBD3 | Epithelia, salivary ducts | hBD1 | DHYNCVSSGGQCLYSACPIFTKIQGTCYRGKAKCCK | hBD1: Poor antibacterial hBD2, hBD3: S. mutans, Streptococcus sanguinis, F. nucleatum, P. gingivalis, C. albicans |
4-6,50) |
hBD2 | PVTCLKSGAICHPVFCPRRYKQIGTCGLPGTKCCKKP | ||||
hBD3 | GIINTLQKYYCRVRGGRCAVLSCLPKEEQIGKCSTRGRKCCRRKK | ||||
Histatins | Salivary glands/ducts | HTN1 | MKFFVFALVLALMISMISADSHEKRHHGYRRKFHEKHHSHREFPFYGDYGSNYLYDN | C. albicans S. mutans | 9,10) |
HTN3 | MKFFVFALILALMLSMTGADSHAKRHHGYKRKFHEKHHSHRGYRSNYLYDN | ||||
HTN5 | DSHAKRHHGYKRKFHEKHHSHRGY | ||||
Adrenomedullin | Epithelium | YRQSMNNFQGLRSFGCRFGTCTVQKLAHQIYQFTDKDKDNVAPRSKISPQGY-NH2 | P. gingivalis S. mutans | 52) | |
Azurocidin | Neutrophil | NQGRHFCGGALIHARFVMTAASCFQ | Gram-negative bacteria, Enterococcus hirae (previously known as Streptococcus faecalis ATCC8043) | 53) | |
Calprotectin | Neutrophils, monocytes, macrophages, mucosal keratinocytes | Calprotectin A | MLTELEKALNSIIDVYHKYSLIKGNFHAVYRDDLKKLLETESPQYIRKKGADVWFKELDINTDGAVNFQEFLILVIKMGVAAHKKSHEESHKE |
P. gingivalis | 28) |
Calprotectin B | TSKMSQLERNIETIINTFHQYSVKLGHPDTLNQGEFKELVRKDLQNFLKKENKNEKVIEHIMEDLDTNADKQLSFEEFIMLMARLTWASHEKMHEGDEGPGHHHKPGLGEGTP | ||||
Lactoferrin | Acinar cells | GRRRSVQWCAVSNPEATKCFQWQRNMRKVRGPPVSCIKRDSPIQCIQAIAENRADAVTLDGGFIYEAGLAPYKLRPVAAEVYGTERQPRTHYYAVAVVKKGGSFQLNELQGLKSCHTGLRRTAGWNVPIGTLRPFLNWTGPPEPIEAAVARFFSASCVPGADKGQFPNLCRLCAGTGENKCAFSSQEPYFSYSGAFKCLKDGAGDVAFIRESTVFEDLSDEAERDEYELLCPDNTRKPVDKFKDCHLARVPSHAVVARSVNGKEDAIWNLLRQAQEKFGKDKSPKFQLFGSPSGQKDLLFKDSAIGFSRVPPRIDSGLYLGSGYFTAIQNLRKSEEEVAARRARVVWCAVGEQELRKCNQWSGLSEGSVTCSSASTTEDCIALVLKGEADAMSLDGGYVYTAGKCGLVPVLAENYKSAQSSDPDPNCVDRPVEGYLAVAVVRRSDTSLTWNSVKGKKSCHTAVDRTAGWNIPMGLLFNQTGSCKFDEYFSQSCAPGSDPASNLCALCIGDEEGENKCVPNSNERYYGYTGAFRCLAENAGDVAFVKDVTVLQNTDGNNNEAWAKDLKLADFALLCLDGKRKPVTEARSCHLAMAPNHAVVSRMDKVERLKQVLLHQQAKFGRNGSDCPDKFCLFQSETKNLLFNDNTECLARLHGKTTYEKYLGPQYVAGITNLKKCSTSPLLEACEFLRK | P. gingivalis, Prevotella intermedia, S. mutans, Candida species | 29,30,54) |
hBD: human β-defensin-3.
Human β-defensin-3 (hBD3) is a natural AMP composed of 45 amino acids, with broad-spectrum activity against bacteria and fungi4-6). Ahn et al.50) investigated the effects of the C-terminal 15 amino acids of hBD3 (hBD3-C15) on S. mutans biofilm formation. hBD3-C15 inhibits bacterial growth, displays bactericidal activity, and reduces biofilm formation in a dose-dependent manner. Additionally, hBD3-C15 enhances the antimicrobial and antibiofilm effects of calcium hydroxide and chlorhexidine digluconate, which are commonly used dental disinfectants. hBD3-C15 also inhibits biofilm formation of S. mutans, Enterococcus faecalis, and Streptococcus gordonii on human dental slices, demonstrating its potential against dental caries and endodontic infections50).
Various modified synthetic AMPs have been developed using natural AMP templates by incorporating different charges, hydrophobicity, chain lengths, amino acid sequences, and amphipathicity57,58). Recently, research has focused on utilizing AMPs produced by other organisms to eliminate oral pathogens. Additionally, efforts are being made to use synthetically designed AMPs to treat oral pathogens. Consequently, researchers are developing synthetic AMPs with promising stability and biocompatibility. Therefore, synthetic AMPs have the potential to serve as alternatives to traditional antimicrobial therapy59).
To design effective synthetic AMPs, understanding the structure-function relationship of AMPs is essential60). The hydrophobicity of AMPs is a critical factor in their ability to permeabilize cell membranes, and the arrangement of hydrophobic regions is crucial for linking AMP structures to their activity60,61). Amphiphilicity, which refers to the presence of distinct polar and nonpolar regions, is key to antimicrobial activity62). Charge is another significant characteristic that affects the activity of cationic AMPs63). Through non-specific electrostatic interactions, positively charged residues bind to the anionic head groups of membrane phospholipids63). Many AMPs are rich in cationic amino acids such as arginine and lysine64). Additionally, positively charged residues near the carboxy-terminus can aid AMP insertion into the outer membrane surface63,64). Specifically, arginine residues are associated with increased membrane insertion and translocation compared with lysine or histidine, partly because of the ability of guanidinium groups to form hydrogen bonds with the hydrophobic core of the lipid bilayer65). The insertion of AMPs into the inner core of the membrane lipid bilayer is heavily influenced by hydrophobic interactions between residues such as proline and tryptophan and hydrocarbon phospholipid tails66). The hydrophobicity of a peptide is directly correlated with its activity60). The secondary structure of AMPs depends on interactions in the peptide backbone, as well as partitioning-folding coupling67). AMPs are disordered in aqueous solutions and typically adopt an α-helical or folded conformation (containing antiparallel β-sheets) in membrane-mimetic environments67,68).
The mechanisms of action of AMPs are concentration-dependent69). Various models have been proposed to describe transmembrane pore formation. The barrel-stave model is based on the interaction of the hydrophobic region of the peptide with the hydrocarbon core of the lipid bilayer70). In contrast, the toroidal model is formed through the interaction between the hydrophilic region of the peptide and the charged phospholipid heads on the membrane surface70). The carpet model is associated with the disruption of the cell membrane through micelle formation and is observed to be concentration-dependent4). Membrane depolarization describes the process of electroporation, in which pores are formed by changes in the external electric field of the membrane70,71). This amphipathic structure is crucial for AMPs to penetrate membranes and form hydrophobic channels or pores12,58,72,73). Amphipathic AMPs attack membranes by interacting with hydrophobic lipids73).
Step 1: Cationic AMPs bind to the negatively charged surfaces of gram-negative (outer membrane) or gram-positive (cell wall) bacteria14,15,74,75). Step 2: AMPs accumulate on the bacterial membrane surface and adopt a stable secondary structure14,75,76). Step 3: As the peptide-to-lipid ratio on the bacterial membrane increases, the AMP hydrophobic region gradually interacts with the phospholipid heads of the bacterial membrane75,76). Step 4: When AMPs reach a threshold concentration, they disrupt the bacterial membrane, causing cell lysis14,15,74-76). However, AMPs may also act intracellularly by inhibiting DNA, RNA, or protein synthesis14,77,78).
Strategies to enhance antimicrobial activity include the design of novel AMPs79,80). The rational design of novel AMPs aims to elucidate the mechanisms of action, such as the extent of membrane disruption, and to explore the relationship between the structural elements of the peptide and its activity81,82). This is particularly important given the occasional need for high concentrations in natural forms and the relative cost of solid-phase peptide synthesis79,82,83). Common synthetic strategies include: 1. cyclization of linear regions; 2. D-amino acid substitution to evade protease recognition and subsequent degradation; and 3. replacement of hydrophobic residues to study the effects of hydrophobicity and amphiphilicity on cytotoxicity58,83). Stability and cytotoxicity are two important issues related to the design of synthetic AMPs for medical applications84). First, it is crucial to protect AMPs from proteases in biological systems85). Various approaches include the insertion of artificial amino acids, cyclization, modified amino and/or carboxyl terminals, non-peptidic backbones (peptidomimetics), and multimerized AMPs38,58,59,86). Although AMPs can non-selectively kill bacteria, selective killing of specific bacteria, such as S. mutans, is feasible by creating a specific competence-stimulating peptide for S. mutans.
We have compiled and reviewed AMPs, including synthetic AMPs, that target oral pathogens but are derived from sources outside the oral environment (Table 2)51,80,87-113). Below are notable examples. Franzman et al.87) conjugated sheep myeloid AMP (SMAP) 28 with rabbit immunoglobulin G (IgG) to demonstrate its antibacterial effect against specific bacteria. Their study showed that the IgG-SMAP28 conjugate exhibited concentration-dependent specificity for P. gingivalis in a solution containing P. gingivalis, A. actinomycetemcomitans, and Peptostreptococcus micros87). This finding suggests the potential for developing antibiotics that target specific oral pathogens, reducing side effects associated with broad-spectrum antibiotics.
Antimicrobial Peptides with Antibiotic Activity Against Oral Pathogens
Peptide name | Origin | Peptide sequence | Target | References | |
---|---|---|---|---|---|
IgG-SMAP28 | Conjugation between SMAP and rabbit IgG | SMAP28 | RGLRRLGRKIAHGVKKYGPTVLRIIRIA- NH2 | Porphyromonas gingivalis | 87) |
KSL | Synthetic peptide | KKVVFKVKFK-NH2 | Streptococcus mutans | 80,88) | |
D-Nal-Pac-525 | Synthetic peptide | Ac-K-Nal-RR-Nal-VR-Nal-I-NH2 Nal=β-naphthylalanines | Streptococcus gordonii | 89) | |
Nal-P-113 | Synthetic peptide | AKR-Nal-Nal-GYKRKF-Nal | S. gordonii Fusobacterium nucleatum P. gingivalis | 90) | |
Pep-7 | Synthetic peptide | RPHGAGEGIDRVPAGP-SPSEVGLAIPSGK | P. gingivalis | 91) | |
GH12 | Synthetic peptide | GLLWHLLHHLLH-NH2 | S. mutans Streptococcus salivarius Streptococcus sobrinus | 92) | |
ZXR-2 | Synthetic peptide | FKIGGFIKKLWRSLLA | S. mutans | 93) | |
DP7 | Synthetic peptide | VQWRIRVAVIRK-NH2 | P. gingivalis | 100) | |
PLNC8 αβ | Lactobacillus plantarum | PLNC8α | DLTTKLWSSWGYYLGKKARWNLKHPYVQF | P. gingivalis | 94,95) |
PLNC8β | SVPTSVYTLGIKILWSAYKHRKTIEKSFNKGFYH | ||||
AmyI-1-18 | Oryza sativa | AAPDIDHLNKRVQRELIG | F. nucleatum P. gingivalis | 96,97) | |
LF-1 | Synthetic peptide (derived from lactotransferrin) | WKLLRKAWKLLRKA | S. mutans | 99) | |
K4-S4(1-15)a | Frog skin | LWKTLLKKVLKAAA-NH2 | S. mutans | 51) | |
C16G2 | Synthetic peptide | TFFRLFNRSFTQALGKGGGKNLRIIRKGIHIIKKY-NH2 | Streptococcus species, although this was specifically designed to target S. mutans | 101) | |
Temporin-GHa | Frog hylarana guentheri | FLQHIIGALGHLF | S. mutans | 102) | |
GHaR | Frog hylarana guentheri | FLQRIIGALGRLF | S. mutans | 102) | |
GHa11R | Frog hylarana guentheri | FLQHIIGALGRLF | S. mutans | 102) | |
Active casein antimicrobial peptide mixture (CAMPs) | Milk casein | β-lactoglobulin (41∼56) | AASDISLLDAQSAPLR | S. mutans, P. gingivalis | 103) |
β-lactoglobulin (141∼151) | TPEVDDEALEK | ||||
β-casein (113∼120) | VKEAMAPK | ||||
β-casein (121∼128) | HKEMPFPK | ||||
β-casein (208∼224) | YQEPVLGPVRGPFPIIV | ||||
α-s1-casein (16∼39) | RPKHPIKHQGLPQEVLNENLLRFF | ||||
α-s1-casein (30∼37) | VLNENLLR | ||||
α-s1-casein (110∼119) | LEQLLRLKKY | ||||
α-s2-casein (163∼176) | TKKTKLTEEEKNRL | ||||
α-s2-casein (213∼222) | TKVIPYVRYL | ||||
κ-casein (63∼70) | YYQQKPVA | ||||
Tet213 | Synthetic peptide | KRWWKWWRRC | Staphylococcus aureus, Pseudomonas aeruginosa | 104,105) | |
Magainins | Frog (Xenopus laevis) skin secretions | 1 | GIGKFLHSAGKFGKAFVGEIMKS | P. gingivalis | 106) |
2 | GIGKFLHSAKKFGKAFVGEIMNS | ||||
Nisin | Lactococcus lactis | ITSISLCTPGCKTGALMGCNMKTATCHCSIHVSK | MRSA | 107) | |
Melittin | Bee and wasp venoms | GIGAVLKVLTTGLPALISWIKRKRQQ-NH2 | MRSA, VRE | 108-110) | |
Apamin | Bee and wasp venoms | CNCKAPETALCARRCQQH-NH2 | MRSA | 108,109) | |
Mastoparan | Bee and wasp venoms | INLKALAALAKKIL-NH2 | MRSA | 108,111) | |
Pleurocidin | Pleuronectes americanusskin secretions | GWGSFFKKAAHVGKHVGKAALTHYL | Streptococcus species | 112) | |
Neurokinin A | Excitatory neurons | HKTDSFVGLM | S. mutans, L. acidophilus, E. faecalis, E. coli, S. aureus, P. aeruginosa, C. albicans | 113) | |
Neuropeptide Y | Excitatory neurons | YPSKPDNPGEDAPAEDLARYYSALRHYITRQRY | 113) | ||
Neuropeptides substance P | Excitatory neurons | RPKPQQFFGLM | 113) | ||
Calcitonin gene-related peptide | Excitatory neurons | ACDTATCVTHRLAGLLSRSGGVVKNNFVPTNVGSKAF | 113) |
Hong et al.80) developed the antimicrobial decapeptide KSL, which exhibited broad antimicrobial activity against diverse enteric bacteria. Liu et al.88) evaluated the antimicrobial activity of KSL against S. mutans and C. albicans, focusing on S. mutans. The results showed that KSL effectively inhibited the growth of various oral bacteria and fungi, with S. mutans and Lactobacillus acidophilus being the most susceptible88). Their study also demonstrated that KSL inhibits biofilm formation and reduces pre-formed biofilms88,114).
Li et al.89) designed three synthetic peptides and evaluated their effects on the growth of S. mutans and biofilm formation. Among the three peptides, D-Nal-Pac-525 showed strong antimicrobial activity against S. mutans, with a minimum inhibitory concentration (MIC) of 4 μg/ml and inhibition of biofilm formation at 2 μg/ml89).
Wang et al.90) revealed a novel role for the synthetic cationic AMP Nal-P-113, which demonstrated potent efficacy against periodontal pathogens, including S. gordonii, Fusobacterium nucleatum, and P. gingivalis, representing early, middle, and late colonizers of dental plaque biofilms. Nal-P-113 not only inhibits planktonic bacteria and biofilm formation but also effectively eradicates polymicrobial biofilms. They confirmed that Nal-P-113 perforated bacterial membranes, leading to cell death and biofilm disintegration90).
Suwandecha et al.91) developed an AMP named Pep-7 specifically designed to combat P. gingivalis. Pep-7 was designed to be sufficiently short to compensate for the longer lengths of traditional AMPs used to treat P. gingivalis. In their study, Pep-7 demonstrated potent antimicrobial activity against two pathogenic strains of P. gingivalis by inducing pore formation at the poles of P. gingivalis cytoplasmic membranes91). Pep-7 was non-toxic to periodontal cells over a broad range of concentrations (4.4 to 70.8 μM) and displayed heat stability under autoclave conditions with activity across a pH range of 6.8∼8.591).
Tu et al.92) investigated the antimicrobial activity of the synthetic amphipathic α-helical peptide GH12 against oral streptococci in vitro. GH12 exhibited potent bactericidal activity, with MICs ranging from 6.7 to 32.0 μg/ml92). GH12 effectively inhibits biofilm formation and reduces the metabolic activity of mature biofilms, particularly in S. mutans, S. sobrinus, and Streptococcus salivarius92).
ZXR-2, a synthetic peptide designed by Chen et al.93), shows a broad range of antibacterial activity against a variety of gram-positive and gram-negative oral pathogens, including S. mutans. ZXR-2 inhibits bacterial cell growth and the formation of S. mutans biofilms by disrupting bacterial cell membranes93). The most notable advantage of ZXR-2 is its ability to eliminate bacterial cells rapidly. According to a study by Chen et al.93), a time-course killing assay demonstrated that treatment with ZXR-2 at 4×MIC resulted in the death of most bacterial cells within 5 minutes. Furthermore, even at the MIC, ZXR-2 exhibited a limited hemolytic effect of less than 15%93).
Khalaf et al.95) showed that two strains of Lactobacillus plantarum inhibit the growth of P. gingivalis. The bacteriocin PLNC8 αβ from L. plantarum was effective, binding to P. gingivalis membranes and causing rapid permeabilization94,95). They concluded in their study that both soluble and immobilized forms of PLNC8 αβ may be used to prevent P. gingivalis colonization, complementing the host immune system in defending against periodontitis-associated pathogens94,95).
AmyI-1-18 is a cationic α-helical peptide derived from rice (Oryza sativa)96). Taniguchi et al.96) synthesized 12 analogs of AmyI-1-18 to enhance antibacterial activity. Among the analogs, AmyI-1-18 (N3L) showed the highest antibacterial activity and low hemolytic activity96). Matsugishi et al.97) synthesized an analog of AmyI-1-18, G12R, which inhibits biofilm formation by P. gingivalis and F. nucleatum. It showed significant bactericidal activity, particularly against F. nucleatum97).
Liang et al.98) constructed a short linear peptide, LR-10, inspired by reutericin 6 and gassericin A, which are produced by various commensal bacteria in the oral cavity. Antibacterial assays showed that LR-10 exhibited potent activity against S. mutans (MIC: 3.3 μM) without inducing resistance and was effective under physiological conditions98). LR-10 also demonstrated a higher bactericidal rate than either chlorhexidine or erythromycin. Additionally, LR-10 effectively inhibited biofilm formation and killed biofilm-encased S. mutans at low concentrations (6.5 μM). Hemolytic activity and cytotoxicity tests confirmed that LR-10 maintained its biocompatibility at effective concentrations98).
Feng et al.99) designed LF-1, a synthetic AMP derived from the lactotransferrin functional domain. LF-1 exhibited selective activity against S. mutans with a MIC of 8 μmol/L and altered the membrane potential and hydrophobicity of S. mutans by forming mesosome-like structures on their membrane99).
Various in vivo studies have demonstrated that combining AMPs with conventional antibiotics can result in a synergistic effect115). However, studies specifically targeting oral pathogens remain limited. Fernandes et al.54) showed that co-administering the AMP lactoferrin with the antibiotic amphotericin B exhibited synergistic antifungal activity against Candida species. Similarly, Lobos et al.116) demonstrated in their in vitro study that the combination of the AMP bacteriocin PsVP-10 with antibiotics chlorhexidine and triclosan produced synergistic antimicrobial effects against S. mutans and S. sobrinus.
Synthetic AMPs represent a potential therapeutic strategy for managing oral diseases59). The increase in antibiotic-resistant bacteria due to the overuse and misuse of antibiotics is a significant concern117). Therefore, new approaches are needed to combat antibiotic-resistant bacterial infections. AMPs are promising candidates for the treatment of oral infections13,118). Despite progress over the past 40 years, only a few AMPs have been approved for clinical use13). Several studies have utilized AMPs in antimicrobial mouthwashes, antimicrobial coatings for implants, and dental restorative materials. Because AMPs do not induce antibiotic resistance even with long-term use, they are suitable as coating materials for implants and dental restorative materials119). Recent studies have shown that cationic AMPs are a promising family of antibacterial agents active against oral pathogenic bacteria with a lower propensity for the development of antimicrobial resistance61,64,96,120).
In the context of the oral microbiome, AMPs can target bacteria involved in biofilm formation and have potential applications in the treatment of chronic periodontitis36). Additionally, native oral AMPs can have immunomodulatory effects, making their application potentially useful for controlling dysbiosis and inflammation associated with pathogenic bacteria in the oral microbiome121-123). AMPs originate from a variety of hosts and are diverse in structure and function, with the ability to modify their amino acid composition for broad-spectrum applications as well as targeting specific pathogens84).
Peri-implantitis, an inflammatory condition affecting the hard and soft tissues surrounding dental implants, is the leading cause of implant failure, with a prevalence rate ranging from 28% to 56%124,125). The primary factor contributing to implant failure is microbial infection caused by various oral pathogens. Current treatment approaches, such as laser therapy, surgical resection, and regenerative procedures, have shown limited efficacy126,127). The difficulty in removing plaque from an implant’s rough, threaded surface has led to a growing interest in preventive strategies focused on reducing plaque formation127).
Various physical and chemical strategies have been developed for antimicrobial coatings to enhance biointegration and minimize bacterial adherence to implant materials and subsequent infection. These include organic coatings such as polymers and biomimetic films, as well as inorganic coatings such as titanium oxide128). Among these diverse coating materials, AMPs have attracted significant research interest due to their broad-spectrum antimicrobial activity and multimodal mechanisms of action41). Accordingly, various AMPs have been studied as coating materials for dental implants (see examples in Table 339,40,45,101,104,105,129,130), Fig. 1).
Application Examples of Antimicrobial Peptides in Oral Health and Hygiene
Peptide name | Application | Description | References |
---|---|---|---|
Lactoperoxidase | Toothpaste, mouthwash, and gel | Used as a saliva substitute and showed improvement of xerostomic symptoms and reduction of streptococci | 39) |
GERM CLEAN | Oral spray | Oral spray containing GERM CLEAN showed an inhibitory effect on the initial adhesion, acid production, extracellular polysaccharides production, and biofilm formation of Streptococcus mutans | 40) |
C16G2 | Oral rinse | C16G2 oral rinse showed a decrease in plaque, salivary S. mutans, lactic acid production, and enamel demineralization | 101) |
Tet213 | Dental implant coating | CaP-Tet213 and CaP-HHC36 coating showed antimicrobial activity against Staphylococcus aureus and Pseudomonas aeruginosa | 104,105) |
HHC36 | |||
β-defensin-2 | Coated recombinant human β-defensin-2 on titanium surfaces yielded antimicrobial activities and prevented bacterial colonization | 129) | |
Human β-defensin-3 containing chimeric peptides | Chimeric peptide containing human β-defensing-3 coating prevented biofilm formation by inhibition of initial colonizing Streptococci | 130) | |
LL-37 | Nanopore coating loaded with LL-37 showed diverse antibacterial and osteogenic induction abilities | 45) |
In this review, we investigated the AMPs known to exist in the oral environment and examined the amino acid sequences of synthetic AMPs developed in previous studies targeting oral pathogens. For applications in oral health, AMPs offer clear advantages, as well as challenges that must be addressed. Due to their broad-spectrum activity and low risk of inducing bacterial resistance, AMPs are emerging as promising materials for oral hygiene119,124,125). However, natural AMPs are susceptible to proteases, and compared to small-molecule drugs, AMPs are relatively large and require high concentrations to be effective12,69). Therefore, derivatives based on natural AMPs that exhibit strong antimicrobial activity at low concentrations and resistance to proteolysis need to be developed. Additionally, there is potential for combining newly designed AMPs with traditional antibiotics to create powerful antimicrobial agents.
In the field of dental materials, research on developing implant coatings using not only AMPs but also other functional peptides is actively underway. This includes the development of peptides that enhance osseointegration and improve implant adhesion (Fig. 1).
However, no consensus has yet been reached on the most suitable peptide for dental implant coatings41). This lack of agreement stems from the limited research providing clear evidence on the durability of AMP coatings on implant surfaces and their stability in the oral environment. Future studies addressing these issues are anticipated to position AMPs as a groundbreaking solution for preventing diseases caused by oral pathogens.
None.
Conflict of interest
No potential conflict of interest relevant to this article was reported.
Ethical approval
Not applicable.
Author contributions
Conceptualization: Youn-Soo Shim and Jun Hyuck Lee. Data acquisition: Sehyeok Im. Formal analysis: Sehyeok Im. Funding: Jun Hyuck Lee. Supervision: Youn-Soo Shim and Jun Hyuck Lee. Writing-original draft: Sehyeok Im. Writing-review & editing: Youn-Soo Shim and Jun Hyuck Lee.
Funding
This research was supported by the project titled “Development of potential antibiotic compounds using polar organism resources (20200610, KOPRI Grant PM24030),” funded by the Ministry of Oceans and Fisheries, Korea.
Data availability
Raw data will be provided by the corresponding author upon reasonable request.
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